Motorcycle engine with an always spring biased open exhaust valve

ABSTRACT

An adjustable exhaust port 2-stroke motorcycle engine with a center adjustable exhaust valve or a split center adjustable exhaust valves includes a closing fork. The closing fork or closing arm base portion is screwed or bolted to a control rod shaft. At least one spring is disposed between a surface of an engine cylinder and the at least one transverse post of an exhaust valve. A first end of the at least one spring is in contact with the surface of an engine cylinder or a surface fixed mounted to the surface of the engine cylinder, and a second end of the spring is in contact with or linked to the at least one transverse post. The center adjustable exhaust valve or either or both of a split center adjustable exhaust valves is spring biased to an open position by the at least one spring at all times.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of and claims priority to andthe benefit of co-pending U.S. provisional patent application Ser. No.15/173,029, MOTORCYCLE ENGINE POWER VALVE CONTROL UPGRADE KIT, filedJun. 3, 2016, which application is incorporated herein by reference inits entirety.

FIELD OF THE APPLICATION

The application relates to motorcycle power valves and particularly tocontrol of power valve position.

BACKGROUND

Off-road motorcycling has become a popular sport enjoyed by racers andriders worldwide. The most popular dirt bikes are relatively lightweight motorcycles powered by a high performance 2-stroke engine. Manyof the most popular models are manufactured by the Yamaha MotorCorporation of Japan (U.S. Corp. office in Cypress, Calif.).

Most notable among the Yamaha off-road models is the model YZ250, whichis the bike of choice for at least sixteen different motorcycle,off-road bike, and dirt bike competitions worldwide. The YZ250motorcycle is powered by a 249 cc liquid-cooled 2-stroke engine. TheYZ250 engine has an adjustable exhaust port known as YPVS™™ (YamahaPower Valve System). Another related model, the YZ125 engine has a splitadjustable exhaust port. At low RPM the valves are closed allowing morecompression and port timing producing more torque. As RPM's increase thevalves are opened allowing less compression and port timing producinghigh RPM horsepower.

SUMMARY

According to one aspect, an adjustable exhaust port 2-stroke motorcycleengine with a center adjustable exhaust valve or a split centeradjustable exhaust valves includes a closing fork or closing arm havingat least one fork arm extending from a base portion of the closing forkor closing arm. The closing fork or closing arm has a closing fork baseportion or closing arm base portion screwed or bolted to an adjustableexhaust port control rod shaft adjacent to the center adjustable exhaustvalve or either or both of a split center adjustable exhaust valves. Thecenter adjustable exhaust valve or either or both of a split centeradjustable exhaust valves have at least one transverse post. At leastone spring is disposed between a surface of an engine cylinder and theat least one transverse post. A first end of the at least one spring isin contact with the surface of an engine cylinder or a surface fixedmounted to the surface of the engine cylinder, and a second end of thespring is in contact with or linked to the at least one transverse post.The center adjustable exhaust valve or either or both of a split centeradjustable exhaust valves is spring biased to an open position by the atleast one spring at all times.

In one embodiment, the at least one spring includes a torsion spring.

In another embodiment, the at least one spring includes a compressionspring.

In yet another embodiment, the one end of the compression spring comesinto contact with the surface of an engine cylinder via at least oneintervening washer or plate.

In yet another embodiment, the at least one spring includes an extensionspring.

In yet another embodiment, the one end of the extension spring ismechanically fastened to a cover or wall which is fixed mounted to thesurface of an engine cylinder.

In yet another embodiment, an opposite end of the extension spring is incontact with the at least one transverse post.

In yet another embodiment, the at least one spring includes a leafspring.

In yet another embodiment, the one end of the leaf spring ismechanically coupled to a wall extending from the engine cylinder.

In yet another embodiment, an opposite end of the leaf spring ismechanically coupled to the at least one transverse post via a linkage.

In yet another embodiment, the adjustable exhaust port 2-strokemotorcycle engine is disposed in a YZ125 series motorcycle.

The foregoing and other aspects, features, and advantages of theapplication will become more apparent from the following description andfrom the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the application can be better understood with referenceto the drawings described below, and the claims. The drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles described herein. In the drawings, likenumerals are used to indicate like parts throughout the various views.

FIG. 1 shows an illustration of the left side of a Yamaha Motor Corp.1999 YZ250 motorcycle;

FIG. 2 shows an illustration of the right side of the motorcycle of FIG.1;

FIG. 3 shows an exploded diagram of an exemplary YZ250 motorcycleengine;

FIG. 4 shows an exploded diagram illustrating the linkage push rodassembly;

FIG. 5 is a drawing which illustrates an exemplary YZ250 engine;

FIG. 6 is a drawing showing the center power valve and the side powervalves coupled to the control rod;

FIG. 7A is a drawing showing the opening sequence of the power valvesfrom all power valves closed;

FIG. 7B is a drawing showing the center power valve open and the sidepower valves closed;

FIG. 7C is a drawing showing all power valves open;

FIG. 8A is a drawing showing the closing sequence of the power valvesfrom all power valves open;

FIG. 8B is a drawing showing the center power valve open and the sidepower valves closed;

FIG. 8C is a drawing showing all power valves closed;

FIG. 9 shows the YPVS™ in its original default closed position;

FIG. 10 shows a drawing of the earlier valve assembly, and the laterversion with holder;

FIG. 11A is a drawing showing the closing sequence of the later stylepower valves from all power valves open;

FIG. 11B is a drawing showing the center power valve open and the sidepower valves closed;

FIG. 11C is a drawing showing all power valves closed;

FIG. 12 is a drawing showing the non-contact arrangement of holder overthe top of valve assembly;

FIG. 13 is a drawing that shows a newer version of the power valve wherethe tip is broken off;

FIG. 14 is a drawing that shows spring/tension resistance on thegovernor;

FIG. 15 is a drawing showing another view of the linkage between thegovernor and the control rod;

FIG. 16A is a drawing showing how the center valve is spring biased tothe open position according to the new hitless system;

FIG. 16B shows the center valve of FIG. 16A being held closed againstthe open spring bias;

FIG. 17 shows two different views of one exemplary embodiment of a newhitless closing fork;

FIG. 18 shows another exemplary embodiment of a closing fork;

FIG. 19 shows a comparison of the new upgrade torsion springs to theoriginal torsion springs and the new closing fork to the original linklever;

FIG. 20A is a drawing showing the opening sequence of the power valvesfrom all power valves closed according to the new hitless system;

FIG. 20B is a drawing showing the center power valve open and the sidepower valves closed;

FIG. 20C is a drawing showing all power valves open;

FIG. 21A is a drawing showing the closing sequence of the power valvesfrom all power valves open according to the new hitless system;

FIG. 21B is a drawing showing the center power valve open and the sidepower valves closed;

FIG. 21C is a drawing showing all power valves closed;

FIG. 22 is a drawing showing the new default open position of the centerpower valve assembly;

FIG. 23 shows a flow diagram for a hitless PVS upgrade;

FIG. 24 is a drawing showing an exhaust valve spring bias to open by anexemplary compression spring;

FIG. 25 is a drawing showing an exhaust valve spring bias to open by anexemplary extension spring;

FIG. 26 is a drawing showing an exhaust valve spring bias to open by anexemplary leaf spring;

FIG. 27 is a drawing showing an exploded diagram of an exemplary YZ125motorcycle engine;

FIG. 28A is a drawing showing the new upgrade torsion springs and aclosing arm of the hitless solution;

FIG. 28B is a drawing showing original link lever;

FIG. 29A is a drawing showing a perspective view of another exemplaryembodiment of a hitless closing fork with a single closing arm;

FIG. 29B is a drawing showing a different perspective view of theclosing fork of FIG. 29A;

FIG. 30A is an illustration showing both exhaust valves spring biasedopen;

FIG. 30B is an illustration showing right exhaust valve closed and leftexhaust valve open;

FIG. 31A is an illustration showing left exhaust valve closed and rightexhaust valve open; and

FIG. 31B is an illustration showing both exhaust valves pushed closedagainst their spring bias open.

DETAILED DESCRIPTION

FIG. 1 shows an illustration of the left side of a Yamaha Motor Corp.1999 YZ250 motorcycle. FIG. 2 shows an illustration of the right side ofthe motorcycle of FIG. 1. As described hereinabove, the currentgeneration YZ250 engine has an adjustable exhaust port power valvesystem (PVS) commonly referred to as the YPVS™ (Yamaha Power ValveSystem).

FIG. 3 shows an exploded diagram of an exemplary YZ250 motorcycleengine. The YPVS™ parts fit into the valve housing of cylinder 7. TheYPVS™ parts operate valves 12 and valve assembly 8, a center adjustableexhaust valve, which controls the opening of the exhaust path. Valveassembly 8 includes transverse posts 81 which extend outward from acenter valve stem 83. The posts 81 are typically provided by a commonrod which extends through a transverse cylindrical opening in centervalve stem 83. Shaft 34 supports from left to right, pulley 32,compression spring 36, plate washer 35, torsion spring 31, link lever30, torsion spring 31, plate washer 35, compression spring 36, andpulley 33. Other related parts include holder 9 and link assembly 27.The pair of torsion springs 31 spring bias side valves 12 to a valveclosed position. At low RPM the three power valves (valve assembly 8,and the two side valves 12) are closed allowing more compression and aport timing which produces more torque. As RPM's increase, the valvesare opened allowing less compression and port timing producing higherRPM horsepower.

The YPVS™ is controlled by a governor that is gear driven directly offthe crankshaft. Centrifugal weights in the governor overcome springpressure and move a linkage.

FIG. 4 shows an exploded diagram illustrating the linkage push rodassembly 47. The push rod assembly 47 couples to shaft 34 (FIG. 3) viaoil seal 45, a keyed opening 477 in the top linkage arm 475 of thelinkage push rod assembly 47, and is affixed to shaft 34 by flange bolt43 and plate washer 44. The push rod assembly 47 lower linkage arm 473is linked to the top linkage arm 475 via a pinned pivot point 479. Lowerlinkage arm 473 couples to the governor (not shown in FIG. 4) viagovernor fork 48 and rotates about oil seal 46.

FIG. 5 is a drawing which illustrates an exemplary YZ250 engine 500. Thecontrol rod shaft 34 controls the positions of power valves 12, andvalve assembly 8. The push rod assembly 47 can be seen linking thegovernor 505 to shaft 34 as described hereinabove. The linkage movesthrough many points and pivots from the governor about pinned pivotpoint 479 up the right side of the engine to the power valve controlrod. When the linkage moves, it rotates the control rod (shaft 34) thatoperates a two-stage power valve system which includes valve assembly 8,and the two side valves 12.

The first stage of the YPVS™ includes a main center valve (valveassembly 8) that operates in the first half of the linkagetravel/control rod rotation. The second stage consists of two sidevalves (power valves 12, one on each side) that are controlled togetheras a pair in the second half of the control rod (shaft 34) rotation inresponse to the linkage travel. Because there are two stages to theYPVS™, each stage operating in a different half of the control rodrotation, Yamaha had to make a flexible connection for the main centervalve. This was done by sandwiching the main center valve between thelegs of a very stiff tension spring. There is one spring (torsionalspring 31) on each side of the main center valve assembly 8. Thesetorsion springs 31 are fixed to the control rod (shaft 34) by means ofthe link lever 30.

FIG. 6 is a drawing showing the center power valve and the side powervalves coupled to the control rod with reference designators labeledaccording to FIG. 3. Pulley 32 (left side) and pulley 33 (right side)can be seen to operate power side valves 12 on each side via the arms276 and pivot points 277 of linkage 27 (FIG. 6).

Opening the valves: FIG. 7A, FIG. 7B, and FIG. 7C show shaft 34 rotatingfrom all valves closed to all valves open. An Allen key 727, not part ofthe YPVS™, was inserted into a hole in shaft 34 to rotate the shaftthrough the three positions of FIG. 7A, FIG. 7B, and FIG. 7C. FIG. 7Ashows all valves closed. In FIG. 7B, one leg of the stiff torsionsprings (torsion springs 31) pulls the main center valve open by actingagainst transverse post 81 until valve assembly 8 hits its stop (halfwaythrough the control rod rotation). Transverse posts 81 are typicallypresent as a single rod which extends through valve stem 83 and extendoutwards from center valve stem 83. As can be seen in FIG. 7C, after themain center valve (valve assembly 8) hits its stop (outward mosttravel), the stiff torsion springs (torsion springs 31) open up to allowthe control rod to continue rotating operating the second stage (sidevalves 12) in the second half of control rod rotation (shaft 34).

Closing the valves: FIG. 8A, FIG. 8B, and FIG. 8C show shaft 34 rotatingfrom all valves open to all valves closed. FIG. 8A shows all valvesopened. In FIG. 8B, the stiff torsion springs (torsion springs 31) arerelieved as the governor pulls the second stage (side valves 12) closed(at half rotation of shaft 34). As can be seen in FIG. 8C, then theother legs of the stiff torsion springs (torsion springs 31) push themain center valve assembly 8 closed.

FIG. 9 shows the YPVS™ in its original default closed position. When thelinkage is disconnected from the control rod, the default position isall valves closed.

Yamaha changed the YPVS™ in 2003. Some reports were that when the maincenter valve was closed, exhaust pressure would push the valve openagainst the stiff tension springs and cause it to flutter. The flutterwas thought to cause a poor low RPM performance, and in some extremecases caused the main center valve to break.

FIG. 10 shows a drawing of the earlier valve assembly 8, and the laterversion with holder 1001. Yamaha changed the tip of the main centervalve to accommodate a holder 1001 that would engage the top of thevalve (valve assembly 8) only after full closed position. This changewas to prevent the main center valve from fluttering in the closedposition.

FIG. 11A, FIG. 11B, and FIG. 11C show valve assembly 8 of the laterversion YPVS™ with holder 1001 rotating from all valves open to allvalves closed. FIG. 11A shows all valves open. In FIG. 11B, the stifftorsion springs (torsion springs 31) are relieved as the governor pullsthe second stage (side valves 12) closed (at half rotation of shaft 34).As can be seen in FIG. 11C, then the other legs of the stiff torsionsprings (torsion springs 31) push the main center valve assembly 8closed. Holder 1001 can be seen over the top of valve assembly 8 whereit prevents valve assembly 8 from opening.

FIG. 12 shows a non-contact arrangement of holder 1001 over the top ofvalve assembly 8.

The FIG. 10 solution was also problematic, because if the holder came incontact with the main center valve before full closed position it wouldbreak the new tip off from the main center valve.

FIG. 13 shows a drawing illustrating a newer version of the power valve(valve assembly 8) where the tip is broken off. After replacing thevalve multiple times most people would leave it broken because it wouldthen operate the same as the prior years and the difference was said tobe insignificant for most riders.

The “HIT” problem: A common problem on later model (1999+) motorcyclesis that the linear governor of the YPVS™ system works smoothly throughthe first half of its travel then it suddenly encounters a significantoutside force/resistance for the second half of its travel. Themotorcycle driver experiences a smooth acceleration for the first halfof the RPM range then a noticeable hesitation where a resistance-forceis encountered. When that resistance-force is overcome, the second stageof the YPVS™ opens releasing a large surge of power or a “HIT”. Thus themotorcycle driver experiences smooth operation—then hesitation—followedby a surge. No amount of tuning, and no presently available productssolve the problem. There is need for a solution to the HIT problem.

Identification of the cause of the HIT problem: It was realized that theHIT problem is caused by the operation of the three valves combined withforce multiplication by the governor linkage.

FIG. 14 is a drawing that shows spring/tension resistance on thegovernor 505. When the main center valve assembly 8 is fully open(halfway through control rod (shaft 34) travel) the force of the twostiff torsion spring (torsion springs 31) opening, along with thefriction of the second stage side valves opening, all create aresistance/force on the control rod (shaft 34) that suddenly startshalfway through its rotation. This combine force is multiplied through amechanical advantage/leverage created by the linkage 47 to the governor505.

FIG. 15 is a drawing showing another view of the linkage 47 betweengovernor 505 and control rod shaft 34 as affixed to the control rodshaft by flange bolt 43.

Solution to the HIT problem: A new “hitless” system as described in moredetail hereinbelow substantially eliminates the outside force acting onthe governor. The hitless solution creates a new connection between themain center power valve assembly 8 and the control rod (shaft 34) thatdoes not add resistance/force to the governor.

In the description which follows, the complete upgraded power valvesystem (PVS) as upgraded operates the valve positions between the closedand opened valve positions with respect to shaft 34 as describedhereinabove. The upgrade includes replacement of the original torsionsprings 31 and installation of a new closing fork part replacing leverlink 30.

The original torsion springs 31 (which spring biased side valves 12closed) are now replaced by different torsion springs. Following theupgrade, new spring bias is opposite, now spring biasing valve assembly8 open.

FIG. 16A and FIG. 16B show a new spring structure (torsion springs 1601)which replaces the original torsion springs 31 (FIG. 3). In the newsystem, two new light torsion springs are slid over shaft 34. However,torsion springs 1601 are not mounted to, nor controlled by the controlrod (shaft 34). One leg of each spring is stopped against the enginecylinder (in some versions, there is a cylinder with a plate attached tothe cylinder on which the leg rests, which we define as included in theuse of the word “cylinder” herein). The other leg of each spring isstopped by the underside of the main center valve. The main center valveis now spring biased to the full open position. In FIG. 16A, it can beseen that before the new closing fork is installed, valve assembly 8 isheld open by the open bias force of spring 1601. Before the new closingfork is installed, valve assembly 8 can be pushed close against the openbias force of spring 1601 by pressing down with a fingertip on the topof valve assembly 8. FIG. 16B shows the center valve of FIG. 16A beingheld closed against the open spring bias. Thus, when partiallyassembled, valve assembly 8 moves to an open position by a new openspring bias technique. Yet, when the new system is fully assembled, theopening and closing operation of side valves 12 with respect to therotational position of shaft 34 remains unchanged.

Closing fork: FIG. 17 shows two different views of one exemplaryembodiment of a new hitless closing fork 1701. The structure of closingfork 1701 includes a flat plate 1702 which extends into two forked arms1703 and a closing fork base portion 1705. A cylindrical through wall1711 from a top surface to a bottom surface of the base portion 1705defines a hole through which a bolt is inserted to secure the upgradekit closing fork 1705 to shaft 34 using an existing threaded hole inshaft 34. The only part of the upgrade kit that is fixed mounted to thecontrol rod is the new closing fork 1701. Closing fork 1701 closes thespring loaded main center valve (spring biased open) from its full opendefault position.

FIG. 18 shows another embodiment of closing fork 1801 having closingforked arms 1803 which extend from a flat mounting plate section 1802.In this embodiment, the closing fork is bolt mount to shaft 34 via aseparate closing fork base section. Shaft 34 slides through acylindrical interior wall section which defines an opening through thebase section under the flat mounting plate section 1802 which extendsinto closing fork arms 1803. Both of the closing fork 1801 and flatmounting plate section 1802 are bolted (bolt 1821) to shaft 34 by use ofthe existing threaded hole in shaft 34. Bolt 1821 extends through acylindrical wall defining a hole in plate 1802 of closing fork 1801(hole and cylindrical wall 1811 not visible in FIG. 18).

The shape of closing fork 1801 can vary without changing the new hitlessclosing fork system and method. For example, during testing, the bevelat the ends of the forked arms was made to avoid making contact with thecover. However, it was found that there was no interference and in mostembodiments, it is now believed that the bevel is not needed.

For initial testing and proof of principle, the closing fork of FIG. 18and the later exemplary valve closing and opening illustrationsaccording the new hitless closing fork system and method were cut andformed from a steel plate stock. The ears were cut off the original linklever 30 and closing fork 1801 was affixed over the modified link lever30. The forked arms 1803 of closing fork 1801 were curved because theflat spot of the modified link lever 30 was not at the correct angle. Itis contemplated that in most embodiments of the forked arms of theclosing fork of either the one-piece embodiment of FIG. 17, or thetwo-piece embodiment of FIG. 18, will be substantially straight as shownin FIG. 17.

In some embodiments it is contemplated that modified link lever 30, oran equivalent replacement base part will be used as a separate base partwhich accepts shaft 34 through a cylindrical walled opening similar tohow the original unmodified link level 30 mounts to shaft 34 (e.g.similar to bolt 1821).

Single closing fork arm: While the closing forks 1701, 1801 both showtwo forked arms, it is contemplated that a closing fork having one armcan be used to provide a hitless control of an adjustable exhaust port2-stroke motorcycle engine as described in the Application. Inembodiments having only one forked arm, it is unimportant where the forkarm is located, only there be a corresponding post 81 or equivalentstructure or flat surface on center valve assembly 8.

FIG. 19 shows a comparison of the new upgrade torsion springs 1601 tothe original torsion springs 31 and the new closing fork to the originallink lever 30;

Opening the valves according to the new system: FIG. 20A, FIG. 20B, FIG.20C show shaft 34 rotating from all valves closed to all valves open.FIG. 20A shows shaft 34 rotated to the all valves closed position.Closing fork 1801 holds valve assembly 8 closed by pressing againsttransvers posts 81 of valve assembly 8 to overcome the open spring biasof spring 1601. FIG. 20B shows shaft 34 rotated so that the forked arms1803 of closing fork 1801 have rotated up allowing the center valveassembly to open by the open bias of spring 1601. FIG. 20C shows shaft34 further rotated to the all valves open position. The operation ofside valves 12 is unchanged by spring 1601 and closing fork 1801modification.

During the valve closed to open progression as described above, thegovernor 505 slowly allows the main center valve (valve assembly 8) toopen until it hits its stop (returning to its full open position halfwaythrough the control rod rotation). The control rod (shaft 34) continuesrotating, operating the second stage (side valves) in the second half ofcontrol rod rotation with no resistance on the control rod caused by anyof the valves or their connections.

Closing the valves according to the new system: FIG. 21A, FIG. 21B, FIG.21C show shaft 34 rotating from all valves open to all valves closed. InFIG. 21A, shaft 34 is shown in the all valve open rotational position.In FIG. 21B, shaft 34 has rotated to the center valve (valve assembly 8)open position and where both side valves 12 are in a closed position.The forked arms 1803 of closing fork 1801 can be seen near or at thetransverse posts 81 of valve assembly 8. In FIG. 21C, shaft 34 hasrotated to the all valve closed rotational position, and the forked arms1803 of closing fork 1801 are pressing against the transverse posts ofvalve assembly 8 to hold the center valve assembly closed.

FIG. 22 is a drawings showing the new default open position of thecenter power valve assembly 8.

During the closing of the valves, the governor pulls the second stage(side valves) closed (at half rotation), then closes the main centervalve with the new closing fork. When the linkage is disconnected fromthe control rod, the default position is all valves open, the oppositeof the original system.

Once modified as described hereinabove, the governor is allowed to movethe control rod and power valves smoothly without any interference tothe governors' linear design. Testing showed this lack of interferencecaused the YPVS™ timing to be a little early, so a new spring with astronger rate was installed in the governor to correct the timing. Thenew governor spring is matched for perfect high RPM performance whileincreasing low RPM performance because of the stronger rate.

The new system as described hereinabove makes the engine output smoothand linear through the entire RPM range with no “HIT”. Followinginstallation of the spring 1601 and closing fork (e.g. closing fork 1801or 1701), there is also an increase of torque in the lower RPM range.The motorcycle engine power valve upgrade kit is believed to work withall types of YPVS™ system main center valves, new style, old style,broken or not from 1999 to the current model year.

Example of a new closing fork and open spring bias of a center powervalve for a hitless control of an adjustable exhaust port 2-strokemotorcycle engine: Reference designators are given for both closing forkversions 1701 (e.g. FIG. 17) and 1801 (e.g. FIG. 18) of the new hitlessclosing fork. The hitless control adjustable exhaust port 2-strokemotorcycle engine closing fork 1701, 1801 includes a flat plate 1702,1802 which extends in a same direction into two substantially parallelflat closing fork arms 1703, 1803. The flat plate 1702, 1802 includes aflat plate interior cylindrical wall which extends perpendicular from afirst flat plate surface to a second flat plate surface to define amounting hole 1711, 1811 which accepts a mounting bolt 1821. A closingfork base section 1705, modified 30, has a mounting internal cylindricalwall in alignment with and to extend the interior flat plate cylindricalwall to allow the mounting bolt 1821 to extend through the closing forkbase section to bolt the hitless control adjustable exhaust port2-stroke motorcycle engine closing fork to a shaft 34. An internalclosing fork base section cylindrical wall 1707 is perpendicular to boththe interior cylindrical wall and a direction of the substantiallyparallel flat closing fork arms to accept the shaft 34 inserted therethrough. Each torsion spring 1601 of two torsion springs has a firstextended leg including an approximately 90-degree bend about where thefirst extended leg extends out from a spring body of each torsion springand a second leg extending straight out of a body of each torsionspring. Each of the torsion springs 1601 is a mirror of each other wherethe first extended leg extends from a different side. The two torsionsprings 1601 define a cylindrical opening which mounts freely androtatingly over a shaft 34 on either side of the closing fork basesection.

FIG. 23 shows a flow diagram for a hitless PVS upgrade as describedhereinabove. The method steps include: A) providing an upgrade kitincluding a closing fork having forked arms, and two torsion springs tospring bias a center adjustable exhaust valve to an open position; B)removing parts of an unmodified power valve shaft which control theoperation a center valve from a shaft including a link lever and twotorsion springs; C) installing the closing fork and the two torsionsprings to over the shaft and securing the closing fork to the shaft byinserting a bolt through the closing fork and threading the bolt into anoriginal threaded hole of the shaft about adjacent to a center exhaustvalve; and D) wherein the installed closing fork and two torsion springsspring bias a center adjustable exhaust valve to an open position for ahitless operation of the power valve system 2-stroke motorcycle engine

Exemplary upgrade kits: In one exemplary embodiment, a power valvesystem (PVS) upgrade kit for the YZ250 Motorcycle includes a closingfork (either a two-piece closing fork with a separate closing fork baseportion, or a one-piece closing fork which includes an integral baseportion) and two tension springs which spring bias the center valve toan open position as described hereinabove, which parts solve the “HIT”problem. There could also be supplied governor compression springs withdifferent rates (spring constants) and an assortment of differentthickness washer plates. There can also be different length pieces ofplastic tube to slide over the governor shaft to control the range ofmotion inside the governor and to limit the amount the side exhaustvalves open. There can also be included a small bushing that can be usedfor shaft 34 as a repair for those who have a worn cylinder shaft hole.

In summary, a new hitless power valve system (PVS) upgrade kit andupgrade method with closing fork system and reversed spring bias isdescribed hereinabove, which solves the HIT problem of hesitation andsurging during power throttle changes.

Alternate Spring Embodiments

Any suitable spring bias can be used to achieve the spring biased openedexhaust valves of the Application. For example, in one embodiment, thespring used to create the spring bias open can be a compression typespring. In compression type spring embodiments, the transverse post canbe removed from the center exhaust valve, and the compression springslid over the valve stem. The transverse post is then reinstalled in thevalve. Upon installation, one end of the compression spring is stoppedby the engine cylinder and the other end stopped by the valvestransverse post, thus creating the spring bias open of the centeradjustable exhaust valve.

In another exemplary embodiment, the spring used to create the springbias open can be an extension spring. One end of the extension springcan be mounted to a surface of the cylinder or valve cover. The otherend of the extension spring can be hooked to the transverse post of thevalve, thus creating the spring bias open of the center adjustableexhaust valve.

In another exemplary embodiment, the spring used to create the springbias open can be a leaf spring. In some embodiments, one end of the leafspring is mounted to a surface of the cylinder or valve cover. The otherend of the leaf spring is hooked to the transverse post of the valve,thus creating the spring bias open of the center adjustable exhaustvalve.

In other embodiments, any suitable spring type can be used to create thedesired spring bias open condition.

FIG. 24 is a drawing showing an exhaust valve spring bias to openembodiment by an exemplary compression spring. Compression spring 2401contacts one or more transverse posts 81 at one end. The other end ofcompression spring 2401 contacts a surface of the cylinder, or one ormore intervening fix mounted parts, the fix mounted parts, mounted toand in contact with a surface of the cylinder. For example, there can beone or more plates and/or washers between the end of compression spring2401 and the surface of the cylinder.

FIG. 25 is a drawing showing an exhaust valve spring bias to openembodiment by an exemplary extension spring 2501. Extension spring 2501is disposed between one or more transverse posts 81 and a fixed surfaceof or in fixed mounted contact with a surface of, or fixed mechanicallycoupled to a surface of the cylinder (not shown in FIG. 25). Forexample, any suitable fastener, such as a screw 2503 can be in contactwith a cover or bracket (not shown in FIG. 25) attached or otherwisefixed mounted to a surface of the cylinder.

FIG. 26 is a drawing showing an exhaust valve spring bias to openembodiment by an exemplary leaf spring 2601. Leaf spring 2601 isdisposed between one or more transverse posts 81 and a surface of thecylinder or any fix mounted part to a surface of the cylinder, such as,for example, a wall, bracket, post, etc. In the example of FIG. 26, oneend of the leaf spring is mechanically coupled to a transverse post 81by a linkage 2603. The other end of leaf spring 2601 is mechanicallycoupled to a wall which is in fixed mounted relation to the cylinder bya screw 2609. Any suitable fasteners can be used to affix either end ofthe leaf spring 2601 to either or both of the linkage and fixed mountingsurface.

Fixed Mounted to a Surface or in Contact with a Surface

Fixed mounted to a surface or in contact with a surface, such as whereone end of a spring is fixed mounted to a surface of the cylinder isdefined to include any intervening fix mounted structures to a surfaceof the cylinder. For example, a bracket, washer, plate, fixed mounted toa surface of the cylinder are understood to create a fixed mountmechanical coupling (one end of a spring mechanically bound to, or incontact with) of one end of a spring to the surface of the cylinder. Thedefinition of fixed mounted to a surface of the cylinder does notinclude, for example, (See FIG. 19, “EXISTING SYSTEM”) a torsion springof the prior art which is fixed mounted by at least one point of thetorsion spring to a shaft which rotates not freely, but with therotation of the shaft, with respect to a surface of the cylinder.

Closing Fork and Closing Arm

Generally, the new concept of the Application includes a closing forktype device, such as, for example, the exemplary closing fork of FIG.17. As described originally, there can be a closing fork with one arm ascompared to the two armed closing fork for FIG. 17. For clarity, aclosing fork with one arm is sometimes interchangeably referred to as aclosing arm.

Applications

The exemplary embodiments described hereinabove introduced the hitlesssolution by a main or center exhaust valve spring bias open in terms ofmotorcycle engines, such as for example, the classic Yamaha YZ-2502-stroke motorcycle engine. Other suitable applications can include, forexample, engines for ATV's, snowmobiles, jet skis, other watercraft,etc.

The same hitless solution concept applies to split center exhaustvalves, such as, for example, has been used in the YZ125 2-strokeengine.

YZ125 2-Stroke Engine

Another exemplary 2-stroke engine which can benefit from the exhaustvalve spring bias open solution is the YZ125 2-stroke engine. The YZ125motorcycle is powered by a 124 cc liquid-cooled 2-stroke engine. TheYZ125 engine has a split center adjustable exhaust valve, probablybecause the exhaust port was too wide for the small cylinder. Thecylinder has a bridge in the middle of the exhaust port to support thepiston with its ring. The center adjustable exhaust valve is split downthe middle with half on each side of the bridge. At low RPM the valvesare closed allowing more compression and port timing producing moretorque. As RPM's increase the valves are opened allowing lesscompression and port timing producing high RPM horsepower.

It was further realized that split center adjustable exhaust valves canbe spring biased to a valves open position at all times, such as, forexample, by the two torsion springs described hereinabove with respectto the adjustable center exhaust valve. For such engines using a splitcenter exhaust valve, a transverse post of each split center exhaustvalve can be engaged by the closing arm upon rotation of the control rodshaft, where the split center exhaust valves close by overcoming an openspring bias provided by the two torsion springs. The new open springbias and closing arm arrangement allows for smooth and precise operationunlike prior art methods with no always present open spring bias.

In some embodiments, the adjustable exhaust port 2-stroke motorcycleengine split center adjustable exhaust valves are a mirror of eachother.

One exemplary adjustable exhaust port 2-stroke motorcycle engine is usedin the Yamaha™ YZ125 series motorcycle.

In alternative embodiments, the springs used to create the spring biasopen can be compression type springs. For example, in some embodiments,the transverse post can be removed from the valves. A compression springis slid over the valve stems. The transverse posts are reinstalled inthe valves. Upon installation one end of the compression springs arestopped by the engine cylinder and the other end stopped by the valvestransverse posts, thus creating the spring bias open of the valves.

In another alternative embodiment, the springs used to create the springbias open can be extension springs. One end of the extension springs aremounted to a surface of the cylinder or valve cover. The other end ofthe extension spring is hooked to the transverse posts of the valves,thus creating the spring bias open of the valves.

In another alternative embodiment, the springs used to create the springbias open can be leaf springs. One end of the leaf springs are mountedto a surface of the cylinder or valve cover. The other end of the leafspring is hooked to the transverse posts of the valves, thus creatingthe spring bias open of the valves.

FIG. 27 shows an exploded diagram of an exemplary YZ125 motorcycleengine. The split center adjustable exhaust valves 2714 and 2715 fitinto the valve housing of cylinder 2706. Valve assemblies 2714 and 2715include transverse posts 81 which extend outward from the center valvestems 83. The posts 81 are typically provided by a common rod whichextends through a transverse cylindrical opening in the valve stems 83.Control rod shaft 2717 supports from left to right, spacer 2727, torsionspring 31, link lever 30, torsion spring 31, and spacer 2727. The legsof the torsion springs 31 straddle the posts on the link lever 30 andall three are connected to the control rod shaft 2717 by screw 2719.Both torsion springs 31 and link lever 30 are forced to rotate with thecontrol rod shaft. The opening in the torsion spring legs straddle thetransverse posts 81 in the exhaust valves. Increased RPM's causegovernor to rotate the control rod shaft 2717 causing torsion springs 31legs to pull the exhaust valves open. Upon decreasing RPM's the governorpulls the control rod shaft 2717 back causing torsion springs 31 legs topush the exhaust valves closed.

Erratic power output is a common problem on later (1999+) motorcycles asthe exhaust valves are able to flutter and even resist opening andclosing due to being sandwiched between the legs of the torsion springsfixed to the control rod shaft. The motorcycle operator experiencesrandom hesitation and surging through changing throttle positions. Noamount of tuning, and no presently available products solve the Erraticoutput. There is need for a solution to the Erratic output problem.

Solution to the Erratic output problem: A new system as described inmore detail hereinbelow substantially eliminates the flutter and softconnection between the control rod shaft and the exhaust valves. The newsolution creates a new direct and positive connection between theexhaust valves and the control rod shaft. The upgrade includesreplacement of the original torsion springs 31 and installation of a newclosing arm part replacing link lever 30.

FIG. 28A and FIG. 28B show a comparison of the new system to theexisting system. FIG. 28A is a drawing showing the new upgrade torsionsprings and a closing arm of the hitless solution. FIG. 28B is a drawingshowing original link lever. The new system shows the new torsion spring2801 structures which replaces the original torsion springs 31 (FIG.27). Each of the new torsion springs 2801 are a mirror of each other oneither side of a single arm closing fork, closing arm 2900. The firstextended leg of each of the mirrored torsion springs 2801 extendsaccordingly from a different side of each torsion spring 2801. The twotorsion springs defining a cylindrical opening which slides freely androtatingly over the control rod shaft 2717 (FIG. 27). Each of thetorsion springs are disposed on either side of the new closing arm 2900base portion 2905. Each of the two torsion springs 2801 having the firstextended leg stopped by and in contact with a surface of an enginecylinder and a second leg stopped by and in contact with a respectivetransverse post of the split center adjustable exhaust valves. The splitcenter adjustable exhaust valves spring biased to a valves open positionat all times by the two torsion springs that are in no way connected tothe control rod shaft.

FIG. 29A and FIG. 29B show two different views of one exemplaryembodiment of hitless closing fork with a single closing arm as aclosing arm 2900. FIG. 29A shows a perspective view of another exemplaryembodiment of a hitless closing fork with a single closing arm 2900.FIG. 29B shows a different perspective view of the closing fork with asingle closing arm 2900 of FIG. 29A. The structure of closing arm 2900includes a flat plate 2903 which extends out past the closing arm baseportion 2905. A cylindrical through wall 2911 from a top surface to abottom surface of the base portion 2905 defines a hole through which abolt is inserted to secure the new closing arm 2900 to shaft 2717 usingan existing threaded hole in shaft 2717. The only part of the upgradethat is fixed mounted to the control rod is the closing arm 2900.Closing arm 2900 closes the spring loaded exhaust valves (spring biasedopen) from their full open default position by overcoming the springbias.

FIG. 30A shows both exhaust valves spring biased open. FIG. 30B showsright exhaust valve closed and left exhaust valve open.

FIG. 31A shows left exhaust valve closed and right exhaust valve open.FIG. 31B shows both exhaust valves pushed closed against their springbias open.

Transverse Posts

In the exemplary embodiment of FIG. 20B, for example, where there is onecenter exhaust valve, typically there are two transverse postsprotruding from either side of the center valve stem 83. Also, asdescribed hereinabove, transverse posts 81 are typically present as asingle rod which extends through valve stem 83 and extend outwards fromcenter valve stem 83. However, it is possible in some embodiments toprovide a single transverse post on either side of the center valve stem83, which can for example, be operated in conjunction with a single armclosing fork.

Or, as is the case in exemplary embodiment of the split center exhaustvalve, valve half has its own center valve stem 83 with its own singletransverse post, and both posts can be operated together, such as forexample, by a common single arm closing fork, or by a two arm closingfork. In other embodiments, two separate closing forks can operate eachhalf of a split center exhaust valve independently of each other.

Once modified as described hereinabove, the exhaust valves move in aprecise manner as the control rod shaft dictates making the engineoutput smooth and linear throughout the entire RPM range with no Erraticcharacteristics.

In summary, a new exhaust valve control system with closing arm and openspring bias is described hereinabove, which solves the Erratic poweroutput problem of surging and hesitation during throttle changes.

Also, in summary, because one end of one or more springs (e.g. one legof one or more torsion springs) is stopped by and in direct contact witha surface of an engine cylinder or a fixed structure attached to thesurface of an engine cylinder, and another end of the one or moresprings (e.g. the opposing leg of one or more torsion springs) is incontact with one or more transverse posts of one or more center exhaustvalve portions (e.g. a single center exhaust valve, or a split centerexhaust valve) such as the transverse posts of a center exhaust valve,the center exhaust valve (or, both parts of a split center exhaustvalve) is spring biased open at all times. Also, the torsion springs aredisposed freely and rotatingly over the control rod, or in the case of acompression spring over valve stem, the spring is disposed freely, butnot necessarily rotatingly over the control rod

By contrast, in the prior art, the torsion springs are mechanicallyaffixed to the control rod, or to a component which is mechanicallyaffixed to the control rod. The rotation of the control rod causes thetorsion springs to rotate. Generally, one leg of the prior art torsionsprings opens the center exhaust valve as driven by the rotation of thecontrol rod, not by spring bias. In the prior art, the torsion springsare not tensioned until the center exhaust valve is fully opened. Then,as the control rod continues to rotate past the center exhaust valvefully opened position, the secondary exhaust valves are opened. As thesecondary valves are opened, the torsion springs of the prior art aretensioned, spring biasing the secondary valves to a secondary valveclosed position.

Applicant realized that previously undesirable engine performancecharacteristics experienced by the motorcycle operator, particularlyduring acceleration, can be solved by changing the mechanical loading onthe governor arm which drives the exhaust valve control rod. In thesolution, described and claimed by the Application, one end of eachspring is stopped by and in direct contact with a surface of an enginecylinder or a fixed structure attached to the surface of an enginecylinder (e.g. one leg of each of the torsion springs in some centerexhaust valve embodiments) is in contact with a surface of the cylinder.Also, instead of being mechanically coupled to the control rod, one ormore springs are disposed between the surface of the cylinder and one ormore transverse posts (e.g. torsion springs are disposed freely androtatingly over the control rod). The control rod no longer directlydrives the center exhaust valve open by driving the legs of the torsionsprings. Rather, as part of the solution, the center exhaust valve isspring biased to the open position at all times.

In the common wisdom of the prior art of adjustable exhaust port2-stroke motorcycle engines, where the center adjustable exhaust valveis driven open by the rotation of the control rod (because the torsionsprings are mechanically coupled to the control rod), and the torsionsprings only become tensioned on rotation past the center exhaust valvefull open position, and then only to bias the secondary exhaust valvesto the valve closed position.

As described hereinabove, the springs used to create the spring biasopen can be of any suitable type, such as, for example, one or morecompression springs, one or more extension springs, one or more leafsprings, etc.

Also, in summary, Applicant generally realized that the solution to thehitless problem is to spring bias open the center exhaust valve, oreither or both sections of a split center exhaust valve by disposing oneor more springs between a surface of the cylinder and at least onetransverse post of the center exhaust valve, or either or both sectionsof a split center exhaust valve where the spring bias open condition isindependent of the rotational position or rotation of the control rod orshaft. For example, in embodiments using one or more torsion springsslid over the control rod or shaft, the spring bias open is independentof the position of the control rod or shaft where the torsion springmoves freely and independently of the control rod or shaft. Similarly,for example, in embodiments where one end of a compression spring is incontact with at least one transverse post and the other end is contactwith a surface of the cylinder either directly or via an interveningplate, washer, etc. Or, where an extension spring is mounted at one endand in contact with a bracket, cover, etc. which is fix mounted to thecylinder and the other end of the extension spring is in contact with atleast one transverse post. Or, where a leaf spring is mounted to and incontact with a bracket, wall, etc. which is fixed mounted to a surfaceof the cylinder and the other end of the leaf spring is mechanicallycoupled to a transverse post by an intervening linkage. In all case, thecenter exhaust valve, or split center exhaust valve is always springbiased open. Also, a closing fork or closing arm can come in contactwith one or more transverse posts to close an exhaust valve (e.g. acenter exhaust valve, or one or both sections of a split center exhaustvalve) by pressing against the always present open spring bias.

It will be appreciated that variants of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be combined intomany other different systems or applications. Various presentlyunforeseen or unanticipated alternatives, modifications, variations, orimprovements therein may be subsequently made by those skilled in theart which are also intended to be encompassed by the following claims.

What is claimed is:
 1. An adjustable exhaust port 2-stroke motorcycleengine with a center adjustable exhaust valve or split center adjustableexhaust valves comprising: a closing fork or closing arm having at leastone fork arm extending from a base portion of said closing fork orclosing arm, said closing fork or closing arm having a closing fork baseportion or closing arm base portion screwed or bolted to an adjustableexhaust port control rod shaft adjacent to the center adjustable exhaustvalve or either or both of the split center adjustable exhaust valves,said center adjustable exhaust valve or either or both of the splitcenter adjustable exhaust valves having at least one transverse post;and at least one spring disposed between a surface of an engine cylinderand said at least one transverse post, a first end of said at least onespring in contact with said surface of said engine cylinder or a surfacemounted to said surface of said engine cylinder, and a second end ofsaid at least one spring in contact with or linked to said at least onetransverse post, said center adjustable exhaust valve or either or bothof the split center adjustable exhaust valves spring biased open by saidat least one spring at all times.
 2. The adjustable exhaust port2-stroke motorcycle engine of claim 1, wherein said at least one springcomprises a torsion spring.
 3. The adjustable exhaust port 2-strokemotorcycle engine of claim 1, wherein said at least one spring comprisesa compression spring.
 4. The adjustable exhaust port 2-stroke motorcycleengine of claim 3, wherein the first end of said compression springcomes into contact with said surface of said engine cylinder via atleast one intervening washer or plate.
 5. The adjustable exhaust port2-stroke motorcycle engine of claim 1, wherein said at least one springcomprises an extension spring.
 6. The adjustable exhaust port 2-strokemotorcycle engine of claim 5, wherein the first end of said extensionspring is mechanically fastened to a cover or wall which is fixedmounted to said surface of said engine cylinder.
 7. The adjustableexhaust port 2-stroke motorcycle engine of claim 5, wherein the secondend of said extension spring is in contact with said at least onetransverse post.
 8. The adjustable exhaust port 2-stroke motorcycleengine of claim 1, wherein said at least one spring comprises a leafspring.
 9. The adjustable exhaust port 2-stroke motorcycle engine ofclaim 8, wherein the first end of said leaf spring is mechanicallycoupled to a wall extending from said engine cylinder.
 10. Theadjustable exhaust port 2-stroke motorcycle engine of claim 8, whereinthe second end of said leaf spring is mechanically coupled to said atleast one transverse post via a linkage.
 11. The adjustable exhaust port2-stroke motorcycle engine of claim 1, wherein said adjustable exhaustport 2-stroke motorcycle engine is disposed in a YZ125 seriesmotorcycle.